Electronic switching device



Sept. 16, 1947. w. P. OVERBECK ELECTRONIC SWITCHING DEVICE Filed Dec.:51, 1943 2 Sheets-Sheetl Milly/7330417) Sept. 16, 1947. w. P. OVERBECK2,427,533

ELECTRONIC SWITCHING DEVICE Filed Dec. 31, 1943 2 Sheets-Sheet 2 I l l lI .merafvl' Patented Sept. 16, 1947 ELECTRONIC SWITCHING DEVICE WilcoxP. Overbeck, Knoxville, Tenn., assignor to Research Corporation, NewYork, N. Y., a corporation of New York Application December 31, 1943,Serial No. 516,409

11 Claims. 1

The present invention relates to electronic switching devices such asare used in counting systems.

The principal object of the present invention is to provide anelectronic switching or counting system capable of operation withsimplified circuits and capable of reliable high speed Operation.

With this object in view, the present invention makes use of transientphenomena in negativeresistance circuits having two conditions ofstability. A number of anodes are arranged for locking in either of twostable conditions. Upon release of the anodes by momentarily cutting offanode current, the anodes follow a prescribed transient behavior bywhich each anode tends to swing over from its original condition to theopposite condition of stability. By proper limitation of the operatingpulse, the original condition may be interrupted at an instant when thebehavior of the system corresponds to the desired switching action; inparticular, by the use of appropriate circuits only a single anode willbe converted from one stable condition to the other under the action ofa pulse applied to the system. The negative-resistance characteristic ispreferably obtained by secondary emission phenomena.

One of the principal advantages of the present invention is that itgives a reliable counting system with utmost simplicity of externalcircuits. A single control electrode may be used for initiating thestepping action for all the anodes, thus avoiding the use of primingcircuits, transfer circuits and the like.

In the accompanying drawings, Fig, 1 is 2. diagram of the preferred formof counting tube embodied in a decimal counting system; Fig, 2 is adiagram illustrating the conditions of stability of the secondaryemission anodes; Fig. 3 is a diagram of the equivalent circuit of theanode; Fig. 4 is a diagram illustrating the transient behavior of theanode circuits; and Fig. 5 is a diagram of a modified form of systemutilizing individual tubes.

The system shown in Fig. 1 comprises a counting tube [0, a pulsingcircuit indicated generally at 12, and a recycling circuit indicatedgenerally at I 4.

The tube I comprises a cathode l6, indirectly heated in any suitablemanner, as by a filament, a control grid l8, a screen grid 20, and aplurality of anodes 22. For counting in the decimal system, ten anodesare used. The cathode is grounded. The control grid is connected to thepulsing circuit by a connection 24, which is connected through aresistor 25 to ground. The screen'grid is connected through a resistor26 with a source of positive potential Ea. The anodes are separatelyconnected to the junctions of a series of resistors 28. A glow lamp 30may be included in series with each resistor 28 for purposes to be laterdescribed. Th first resistor 28 is connected to the positive source Ea.There is one resistor 28 (and glow lamp 30, if used) ahead of eachanode. A resistor 3| connected to the last anode leads to the recyclingcircuit M, as will be described later.

The tube l0 makes use of secondary emission phenomena. With fixedpotentials on the control grid and screen grid, the current-voltagecharacteristic of any anode is represented by Fig. 2. At zero anodepotential, electrons flow from the cathode to the screen grid and nonereach th anode, so that the anode current is zero. If a slight positivepotential is applied to the anode, it robs the screen grid of someelectrons, and there is a positive anode current. The velocity ofelectrons arriving at the anode is determined by the anode potential,and as the potential increases, the electron velocity likewiseincreases. At higher anode potentials, the electrons arriving at theanode have suflicient velocity to knock secondary electrons loose fromthe anode surface, and these secondary electrons are drawn to the screengrid. The resultant anode current is determined by the differencebetween the number of primary electrons arriving at the anode and thenumber of secondary electrons leaving it. The positive anode currentreaches a maximum at a certain potential a, beyond which thecharacteristic has a negative lope. At a certain anode potential,indicated at b, the value of which depends on the character of the anode(about volts with a stainless steel anode), there are as many electronsreleased from the anode as are received by it, so that the resultantanode current is zero.

As the anode potential increases beyond b, each primary lectron canrelease more than one secondary electron, and the anode current becomesincreasingly negative, reaching a minimum at c. The part of the curvebetween a and c is the negative-resistance portion of thecharacteristic. As the anode potential increases further and approachesthe screen grid potential, fewer secondary electrons are drawn to thescreen grid, and the anode current rises towards zero. When the anodepotential exceeds the screen grid potential, the secondary electrons nolonger are anode potential is plotted against time.

drawn to the screen and the anode current returns to a positive value,made up only of primary electrons. In Fig. 2, the screen grid potentialis chosen to be about three times the zero-current potential b, which issatisfactory for the present invention.

If there is a resistance in series with the anode, the operation isindicated by the diagonal straight line in Fig. 2, the slope of the linedepending on the resistance. This dotted line intercepts the anodecharacteristic at two stable points, corresponding to anode potentialsE1 and E2, lying respectively to the left and right of points a and c. Asecondary-emission tube with series resistance must lock in at eitherone of these points. This constitutes an elemental trigger circuit.

In the arrangement of Fig. 1, each anode operates on a characteristicsuch as that shown in Fig. 2. It has been found that the secondaryemission effect for each anode is substantially independent of thepotentials on the other anodes. It is, therefore, possible to haveadjacent anodes in opposite conditions of stability, which conditionswill be maintained so long as the screen grid and control gridpotentials are maintained at constant values.

The operation of the tube Ill as a counting device will first bedescribed on the assumption that negative input pulses are applied tothe connection 24. The pulsing circuit l2, by which the pulses areapplied, will be described later in detail. For simplicity of initialexplanation, let us consider a system in which the glow lamps 30 are notused. First let us assume that all anodes are locked at the lowpotential E1, at which potential the current to each anode is positiveas determined mainly by primary electron flow. It will be observed thatthe system comprises a ladder-type network in which the series elementsare the resistors 28 and the parallel elements are the capacitances 32of the anodes to ground, as illustrated diagrammatically in Fig. 3. If anegative pulse is applied to the control grid l8, thus tending to. cutoff anode conduction, all of the anodes tend to rise in potential, butthe first one rises most rapidly. This action is illustrated by graphsof the transient phenomena illustrated in Fig. 4, in which The potentialof the first anode starts to rise from E1 along the curve 34. If thenegative potential were held on the control grid indefinitely, the

anode potential would rise along the dotted portion 34' of the curveuntil the anode potential ultimately reached E2. The shape of the curve34, 34' may be determined approximately by the transient solution forthe resistor 28 in series with the capacitance 32 between the firstanode 22 and ground.

The conditions for the second anode are determined by the fact that itsresistor 28 and its capacitance 32 are connected across the capacitance32 between the first anode and ground, so that the rise of potential onthe second anode is retarded by the necessity for charging the firstcapacitance. Hence its potential rises from E1 along a curve 36, whichis below the curve 34. If the negative control grid potential were heldindefinitely, the anode voltage would follow the dotted curve 36, andeventually reach E2. A similar transient characteristic might be drawnior each of the remaining anodes, and each such characteristic would liebelow-the curve 36, 36.

The invention contemplates that the negative potential applied to thecontrol grid is not continued indefinitely, but is in the form of apulse, terminating at a time h. The duration of this pulse is selectedso that the curve 34 for the first anode will have risen above a-certaincritical potential which determines that the anode will swing over tothe high potential condition, while the potential of the second anodewill not have risen to such critical potential. In Fig. 4, the criticalpotential which determines whether a particular anode will swing to thehigh or the low stable potential is assumed to be the same as thezero-current potential 17. At the termination of the pulse, therefore,the first anode will go immediately to the second stable conditionrepresented by E2, this rise of potential being indicated by the solidcurve 34". The second anode will return to the initial stable conditionE1 along the solid curve 36". All subsequent anodes being at potentialsbelow that of the second anode will also revert to the stable conditionrepresented by El. The result of the application of the negative pulse,therefore, is that the first anode will be converted to the highpotential condition and the remaining anodes will revert to the lowpotential condition.

On a subsequent negative pulse, the first anode, which now starts at thehigh potential condition, will tend toward the low potential conditionalong the curve 38, which curve has a dotted extension. 38 representingultimate return to E2 if the control grid potential were maintainedsufficiently long at negative potential. At the termination of thepulse, the anode potential rises rapidly along the curve 38 to itsinitial high value E2. The second anode follows a curve similar to thatrepresented by curve 34, 34" to the high potential E2, while allsubsequent anodes drop back to E along curves similar to 36, 36".

In general, therefore, the tube will have none, one, two or more of thefirst anodes at the highpotential condition and all the remaining anodesat the low-potential condition. The application of a negative potentialto the grid l 8 tends to convert each low-potential anode to thehigh-potential condition; that is, if the grid potential were maintainedfor a sufiiciently long time all anodes would arrive at thehigh-potential condition. By limiting the pulse duration, however, thetransient swings of all but one of the initially lowpotential anodes arestopped before the anode potential passes through the critical value b.For only one.anode is the transient allowed to pass through the criticalvalue. Therefore, the resultant action of a pulse of proper duration isto leave all of the original high-potential anodes in the high-potentialcondition, to convert the first low-potential anode to thehigh-potential condition, and to leave all remaining anodes in thelow-potential condition. In other words, each pulse increases by one thenumber of high-potential anodes until all of the anodes arrive at thehigh-potential condition.

The foregoing description of operation is based on the assumption thatglow lamps 30 are omitted. The use of the lamps performs two functions;first, to give an indication of the number of pulses that have beenapplied to the tube, and second, to alter the transient characteristicsof Fig. 4. As for the first function, it will be noted that only one ofthe glow lamps is included between a high-potential and a low-potentialanode, and only that lamp will ignite. The single ignited lamp is anindicator of the number of applied pulses.

The function of the lamp in altering the characteristics of Fig. 4 maybe understood by notlng that a lamp will not ignite until the potentialapplied to it exceeds a certain definite value. Hence, all anodes beyondthe last high-potential anode are at zero potential rather than at E1.This means that the transient characteristic represented by 36 startsfrom a lower point and will not start to rise at zero time, in fact, ifthe pulse is sufiiciently short, the potential of the anode may remainat zero. The characteristics represented by 34 and 38 tend to follow theindicated curves, at least approximately, since for these anodes theignition potential of the glow lamps is rapidly exceeded. The glowlamps, therefore, provide a more reliable action in-efiectivelydiscriminating between the anode that is to. kick over to the highpotential condition and those that are to remain in the low potentialcondition.

Since the operation of the tube It) is most effectively carried out bysharply defined pulses of fairly critical duration, the special pulsingcir- .cuit I 2 is provided. This circuit comprises two pentodes 44 and46, the anodes of which are excited by a. source of positive potentialEb through resistors 48 and 50. The suppressor grids of both tubes aregrounded, and the screen grid of each tube is connected at 52 with theanode of its companion tube. An input circuit 54 including a resistor 55is connected between ground and the control grid of the first tube 44.An alternating potential is applied to the circuit 54. The control gridof the second tube is connected to ground through a resistor 58. Theanode of the first tube 44 is connected through a condenser 60 with thecircuit 24 leading to the control grid of the counting tube Ill.

The tubes 44 and 46 form a binary pair in which one tube is at highanode potential and the other tube is at low anode potential. The anodepotential of the first tube 44 is normally at the high value (anodenon-conducting) and that of the second tube 46 is at the low value(anode conducting). A positive potential applied through the inputcircuit 54 to the control grid of the tube '44 converts the anode of thefirst tube 44 to the conducting (low-potential) condition and that ofthe second tube to the non-conducting (high-potential) condition. Thus anegative pulse is transmitted through the condenser 60 to the grid I8 ofthe counting tube, and it is this pulse which is utilized to operate thecounting tube, as above described. The duration of this pulse isdetermined by the time constant of the circuit composed of the condenser60 and the resistor 25, and the pulse duration is so chosen as to givethe results heretofore described in connection with Fig. 4.

A negative potential applied to the pulsing circuit through 54 resultsin restoring the tubes 44 and 46 to the original condition, and also intransmitting to the counting tube a positive pulse, which, however, hasno efiect on the conditions existing in the counting circuit. Thus, withan alternating potential input at 54, only the positive half-waves arecounted.

In the system thus far described, successive impulses will ultimatelybring all of the anodes 22 to the high potential (E2) condition. Forsubsequent counting operations, it is necessary to restore the countingtube to its original condition,

and this is preferably accomplished automatically by means of therecycling circuit shown at M. This circuit comprises a pentode 62 havingits cathode and suppressor grid grounded, its control grid negativelybiased from a source En through a resistor 64, and its screen gridexcited from the source Eb. The anode is connected to the screen grid 20of the counting tube, whereby the positive potential Ea is applied tothe anode through the resistor 26.

A connection 66 leads from the anode of the second pulsing tube 46through a condenser 68 to the grid of the tube 62. Also, a connectionruns fromthe last anode of the tube I0 through the resistor 3| and aglow lamp 10 to the control grid of the tube 62.

Normally the anode of the tube 62 is nonconducting, because of thenegative bias on the control grid. At the conclusion of each pulsingoperation of the pulsing circuit 12, a positive pulse is applied to thecontrol grid of the tube 62 through the connection 66 and condenser 68.It will be recalled that under the action of a. positive pulse. appliedto the input circuit 54 of the pulsing circuit i2, the second tube 46 isconverted from low to .high anode potential. This conversion sends apositive pulse over the connection 66 and through the condenser 68 tothe grid of the tube 62, at the same time that a negative pulse is beingtransmitted to the counting tube through the condenser 80. positivepulse is insuflicient to overcome the negative bias Ec applied to thegrid, and the tube 62 therefore remains in non-conducting condition.However, if the last anode 22 of the counting tube H] has been broughtto its high potential condition by the action of the negative pulseapplied to the counting tube, conduction will have been establishedthrough the resistor 3| and the glow lamp 70, thus priming the grid oftube 62 so that the last part of the pulse applied through 68 willmomentarily swing the grid to a positive potential. The anode circuit ofthe tube 62 then becomes conducting, and draws sufficient currentthrough the resistor 26 to lower the potential on the screen grid 20 ofthe counting tube. This cuts ofi conduction to all anodes in thecounting tube, and restores all anodes 22 to the potential Er. As soonas that happens, thepriming potential on the grid of the tube 62 isremoved and the non-conducting condition of that tube is restored, sothat the screen grid 20 is brought back to its normally constantpotential.

The foregoing operation of the recycling circuit may be availed of toinitiate operation of any suitable carry-over device for counting in asubsequent stage.

For the separate single tube It], a number of individual tubes 72 ma besubstituted as shown in Fig. 5. These tubes have their cathodes, controlgrids and screen grids connected together and their anodes separatelyconnected to an input network composed of the resistors 28 and'glowlamps 30. The tubes 12 may be otherwise connected with the pulsing andrecycling .circuits, exactly as is the single tube [0 of Fig. 1.

From the foregoing description it will be observed that the countingdevice H! (or the individual tubes 12) forms a counting system in whichone of the principal advantages lies in the simplicity of theconnections. A single external connection to each of the grids l8 and 20is suflicient, and the use of complicated transfer and priming circuitsis avoided. The external circuits for the anodes comprising only theresistors 28 (with or without the glow lamps 30) are exceptionallysimple in their connections. The tube is preferably under very highvacuum and the Ordinarily this potential condition.

, 7 results of the present invention are attained without reliance onionization phenomena.

The switching action in the present invention may be regarded asresulting from the distinctive transient behavior of circuits underdifferent potential conditions. Thus the circuit is converted from onecondition to another by first cutting of! anode current, therebyreleasing the anodes from their original condition of stability andallowing the several anode circuits to follow their natural transientbehavior for a specified time, as indicated in Fig. 4, and thenrestoring the anode current when the instantaneous conditions correspond.to the conversion of a single anode, from a previous low-potentialcondition to the highpotentlal condition. This is, in fact, a specificexample of more general operation. Since the transient characteristicsof the several anodes are quite different from one another, it ispossible, by controlling the pulse duration, to cause other combinationsof efiects; for example, by reference to Fig. 4 it will be seen that bysomewhat increasing the pulse time, it is possible to convert two anodesfrom the low-potential to the high- It will be clear to those skilled inthe art that a variety of selective actions may be obtained.

Having thus described the invention I claim- 1. An electronic switchingsystem comprising a plurality of anodes, common and substantiallyequipotential grid means for the anodes, means for establishingindependent negative-resistance characteristics for the anodes to causeeach anode to assume either a,high-potential or a low-potentialcondition of stability, a network including circuit elements connectedbetween adjacent anodes and independent capacitances between the anodesand ground, whereby a change of potential on any anode results inretarded potential changes on succeeeding anodes, means for applying tothe common grid means a pulse to release all of said anodes from theirstable conditions, the duration of the pulse being limited to causeconversion of selected anodes from one stable condition to the other.

2. An electronic switching systemcomprising a plurality of anodes,common and substantially equipotential grid means for the anodes, meansfor establishing independent negative-resistance characteristics for theanodes to cause each anode to assume either a high-potential or alowpotential condition of stability, a network including circuitelements connected between adjacent anodes and independent capacitancesbetween the anodes and ground, whereby a change of potential on anyanode results in retarded potential changes on succeeding anodes, meansfor applying to the common grid means a pulse to release all of saidanodes from their stable conditions, the duration of the pulse beinglimited to cause conversion of only a single anode from one stablecondition to the other.

3. An electronic switching system comprising a plurality of anodes. eachcapable of stable operation at either high or low anode potential,common and substantially equipotential grid means for releasing all ofsaid anodes from their stable conditions, resistances connected betweenadjacent anodes and forming a network with the capacitances of theanodes to ground, means for applying to the common grid means a pulse torelease all of said anodes from their stable conditions whereby eachanode tends toward the opposite stable condition, the duration of thee.pulse being limited to cause reversion to the orig- 75 -inal stablecondition of anodes which do not pass through a critical potential.

4. An electronic switching system comprising a plurality of secondaryemission anodes each capable of stable operation at either high or lowof selected anodes to their original conditions of stability.

5. An electronic switching system comprising a plurality of anodes,means for establishing primary conduction to the anodes, means forcausing secondary emission from the anodes, whereby each anode isnormally locked in at either a stable high potential or a stable lowpotential, electrical network means associated with the anodes todetermine progressively different transient behavior of the anodes,common and substantially equipotential control grid means, means forapplying a pulse to the grid means for initiating transient operation ofthe anodes, and means for limiting the pulse duration to effectselective conversion of anodes from one stable condition to the other.

6. An electric switching system comprising a plurality of anodes, commonand substantially equipotential grid means for the anodes, means forestablishing independent negative-resistance characteristics for theanodes to cause each anode to assume either a high-potential or alowpotential condition of stability, a network including circuitelements connected between adjacent anodes and independent capacitancesbetween the anodes and ground, whereby a change of potential on anyanode results in retarded potential changes on succeeding anodes, and apulsing circuit for applying to the grid means a pulse tending to cutoif conduction, said pulsing circuit having means for limiting theduration of the pulse to cause conversion of selected anodes from onestable condition to the other.

7. An electronic switching system comprising a plurality of anodes,common and substantially equipotential grid means for the anodes, meansfor establishing independent negative-resistance characteristics for theanodes to cause each anode to assume either a high-potential or alow-potential condition of stability, 2. network including circuitelements connected between adjacent anodes and independent capacitancesbetween the anodes and ground, whereby a change of potential on anyanode results in retarded potential changes on succeeding anodes, meansfor applying to the common grid means a pulse to release all of saidanodes from their stable conditions, the duration of the pulse beinglimited to cause conversion of selected anodes from one stable conditionto the other, said network including devices which become conductingonly under potentials in excess of an ignition potential, whereby thetransient changes on selected anode at initially low potentials areretarded.

8. An electronic switching system comprising a plurality of secondaryemission anodes each capable of stable operation at either high or lowanode potential, common and substantially equipotential grid means forthe anodes, a resistor in series with the first anode and resistorsconnecting adjacent anodes, means for applying a negative pulse oflimited duration to the common grid means, tending to out 01f conductionfrom all anodes and thereby to cause each anode to swing toward theopposite condition of sta-- bility according to a transient, thecharacter of which differs for the successive anodes, the termination ofthe pulse being such as to determine reversion of selected anodes totheir original conditions of stability, said network including deviceswhich become conducting only under potentials in excess of an ignitionpotential, whereby the transient changes on selected anodes at initiallylow potentials are retarded.

9. An electronic switching system comprising a plurality of anodes,common and substantially equipotential grid means for the anodes, meansfor establishing independent negative-resistance characteristics for theanodes to cause each anode to assume either a high-potentialor alowpotential condition of stability, a network including circuitelements connected between adjacent anodes and independent capacitancesbetween the anodes and ground, whereby a change of potential on any anodresults in retarded potential changes on succeeding anodes, means forapplying to the common grid means a pulse to release all of said anodesfrom their stable conditions, the duration of the pulse being limited tocause conversion of only a single anode from one stable condition to theother, and recycling means operable when all anodes are at highpotential to restore them to the low-potential condition.

10. An electronic switching system comprising a plurality of anodes,means for establishing primary conduction to the anodes, means forcausing secondary emission from the anodes, whereby each anode isnormally locked in at either a stable high potential or a stable lowpotential, electrical network means associated with the anodes plying apulse to the grid means for initiating I transient operation of theanodes, and means for limiting the pulse duration to efiect selectiveconversion of anodes from one stable condition to the other, andrecycling means operable when all anodes are at high potential torestore them to the low-potential condition.

11. An electronic switching system comprising a plurality of anodescapable of stable operation at either high or low anode potential,common screen grid means determining secondary emission characteristicsfor the anodes, common and substantially equipotential control gridmeans, pulsing means for applying to the control grid means a negativepulse tending to cut ofi anode conduction and to cause each anode toswing fromits initial toward the opposite condition of stability, saidpulsing circuit having provision for terminating the pulse at a time tocause reversion of selected anodes to their initial conditions, arecycling circuit including a tube having an anode and a control grid,connections from the pulsing circuit and the last anode of the switchingtube to the grid of the recycling tube to cause anode conduction in therecycling tube when thelast anode of the switching tube is at highpotential, and connections between the anode and the recycling tube andsaid screen grid means for momentarily reducing the screen gridpotential and thus to convert all anodes of the switching tube to thelow-potential condition of stability.

WILCOX P. OVERBECK.

REFERENCES CITED UNITED STATES PATENTS Name Date Skellett Aug. 18, 1942Number

